1. Field of the Invention
The invention relates to a structure having a light modulating film, and a light control device using the same.
2. Description of the Related Art
PLZT is a transparent ceramic having a composition of (Pb1-yLay) (Zr1-xTix)O3, and is known as a material having an electrooptic effect. The electrooptic effect refers to the phenomenon that a substance causes polarization with a change in its refractive index when an electric field is applied to the substance. Through the use of the electrooptic effect, it is possible to switch light phase by turning on/off the applied voltage. PLZT thus has such applications as a light control device such as an optical shutter.
For these applications including the optical shutter device, bulk PLZT has been widely used conventionally (Japanese Patent Laid-Open Publication No. Hei 5-257103). It is difficult, however, for optical shutters using bulk PLZT to meet demands for finer configuration, higher integration, lower operating voltage, and lower cost. Besides, the bulk method includes the step of processing a mixture of metal oxides, or materials, at high temperatures of 1000° C. and above. If this method is applied to the device formation processes, a number of constraints will thus be imposed on the selection of the materials, the device structures, and so on.
Under the circumstances, attempts have been made to apply a thin film of PLZT formed on a base member to the light control device, instead of bulk PLZT. A display unit using such a PLZT thin film appears in Japanese Patent Laid-Open Publication No. Hei 7-146657 (paragraphs 0022 to 0044). The publication describes that a PLZT film is formed on a glass or other transparent substrate, comb-shaped electrodes are formed thereon, and the resulting structure is used as an optical shutter that utilizes a quadratic electrooptic effect of PLZT. While this optical shutter realizes a low-voltage-driven display unit having simple configuration and high reliability, it still has room for improvement in terms of the magnitude and stability of the quadratic electrooptic effect.
Meanwhile, as a recording method of large capacity, digital information recording systems using the principle of holography have been receiving attention recently (for example, see Japanese Patent Laid-Open Publication No. 2002-297008). Unprecedented excellent systems can be expected if PLZT-based optical shutters are applied to these systems. This requires, however, an even higher level of performance in terms of the magnitude and stability of the quadratic electrooptic effect. More specifically, the technical challenge of importance is to achieve a PLZT thin film that makes and can stably exhibit a sufficiently large change in the refractive index with respect to predetermined light.
By the way, it has been unfeasible in the conventional level of technology to fabricate a PLZT thin film that shows a high quadratic electrooptic effect with stability. Some device structures require that PLZT be formed on a polycrystalline or amorphous underlayer. In such locations, it is even harder to realize a PLZT thin film that shows a high quadratic electrooptic effect with stability.